The capesize Oil Bulk Ore Carrier mv Derbyshire sank
off Okinawa in Typhoon ORCHID in September 1980 with the loss of 44
lives. The cause of her sinking remained a mystery until 1994 when,
using modern deep-sea underwater techniques an expedition located
the wreck. This preliminary expedition led to a detailed survey of
the wreck in 1997 which revealed aspects of the sinking that showed
- after subsequent research using testing tank models - that the initial
cause of sinking was progressive flooding of forward spaces.
The Derbyshire initially suffered damage to
the air pipes serving the fore peak tank and the forward bosun's store.
The damage was attributed to the impact of heavy seas on air pipes
and, possibly, the displacement of the starboard windlass, which then
caused further damage.
The research that was commissioned subsequent to the findings
at the wreck site showed that large volumes of water can be taken
in through damaged air pipes of the size and type typically fitted
to bulk carriers and tankers to serve forward tanks. Flooding rates
in excess of 400 cubic metres per hour through a single 300 mm air
pipe were found to be possible in relatively heavy but by no means
extreme seas.
Flooding of the fore peak and the forward ballast tank through
air pipes caused the ship to trim by the head and reduce the effective
bow height. Statistical analysis of tank test results indicated that,
although there was a low probability of the ship meeting a hatch-breaking
wave in her intact condition, a reduction in bow height of as little
as 1.1m could lead to a 70% probability of encountering a hatch-breaking
wave (depending on speed, etc). The hatch covers of Nos.1 and 2 cargo
holds subsequently failed allowing rapid flooding of those spaces.
The ship was then in a condition beyond its survival capability.
The evidence considered by the investigation indicated that
these events took place rapidly. There was no evidence that any attempt
to abandon ship had been possible. The events took place almost certainly
at night and it was concluded that in such circumstances the ship's
crew would have been unlikely to have detected the impending disastrous
circumstances until the ship was already doomed.
Masters - particularly those who sail on large ships where
the bridge is remote from the forward spaces - need to be especially
vigilant that the weathertight integrity of their ship is fully maintained.
After initial battening down, regular checks should be made to detect
any reduction in the integrity of the closing arrangements. In particular:
- Spaces that are entered on a routine basis should be subject to
a careful check after their use to ensure that watertight integrity
is fully restored.
- Rope and other hatches should have their fixing arrangements checked
to compensate for any slackening of toggles or other fixing devices.
- Bilges and tanks should be regularly sounded and any ingress of
water investigated.
- Where bilge alarms are fitted, they should be regularly tested.
- Pumping arrangements in forward spaces should be regularly checked
for operational effectiveness.
Owners of ships without bilge alarms in remote forward spaces
should consider fitting such devices with audible and visual indication
on the bridge.
Masters should consider early evasive action in the event
that severe weather systems approach the region in which the ship
is navigating. Due regard should be had to the handling characteristics
of the ship and any limitations of control that may lead to the ship
being dangerously exposed to the forces of such extreme weather.
Masters should keep owners or managers advised when weather
conditions deteriorate necessitating evasive action. Such advice should
include position, course and speed and should be given more frequently
in proportion to the severity of the weather and the limitations imposed
on the ship's progress.